In this article we consider domains able to contain pattern with one or
two elementary cells, i.e. \(L_{x,z}=|n_{x,z}|\lambda _{x,z}\) 
where \(n_x=1\)  or 2 and \(n_z=\pm 1\)  or \(\pm 2\) .
According to [1]}, in PCF wavelength \(\lambda _x\)  is found to be
approximately equal to
110 over the whole range \([R_{\rm g},\,R_{\rm t}]\) , while wavelength
\(\lambda _z\)  varies as a function of \(R\)  in the range \([40,\,85]\) 
These observations serve us to fix the size of the
systems that we are going to consider below.
As shown in [2]}, the specificity of such systems
is to convert the spatio-temporal evolution of fluctuating domains
observed in the neighbourhood of \(R_{\rm t}\)  into the temporal evolution
of coherent patterns characterised by the amplitudes of the corresponding
fundamental Fourier modes; possible orientation changes are associated
with changes of sign of the spanwise wavenumbers. Close enough to
\(R_{\rm t}\) , there is also some probability that featureless turbulence,
the state that prevails for \(R>R_{\rm t}\) , be observed transiently, which
is akin to the intermittent regime identified in [3]}.
In contrast, in the lowest
part of the transitional range, close to \(R_{\rm g}\) , the orientation
remain frozen as expected for well-formed steady oblique bands. We
first illustrate this phenomenon using snapshots of \(\mathbf {u}^2\) 
in Figures REF  and REF .
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